1. Field of the Invention
The present invention relates to fuse circuits for semiconductor devices, and more particularly to fuse circuits used during the fabrication of semiconductor integrated circuits.
2. Description of the Related Art
Several semiconductor integrated circuits may have different electrical characteristics even though they were fabricated using the same fabrication method. This is because it is difficult to continuously maintain uniform conditions during the fabrication of each integrated circuit. Thus, integrated circuits (hereinafter, referred to as "IC"s) fabricated with a particular process have electrical characteristics which deviate from, and are distributed around, a designed target level of electrical characteristics.
The electrical characteristics of many products in which such IC's are used call for a very limited range of electrical characteristics. For example, FM (frequency modulation) carrier & deviation must be managed in an extremely limited range during the fabrication of many products. In an NTSC image signal processing IC for VHS video system, it is clearly stated in the VHS specification for a VCR (video cassette recorder) that, when an image signal of 0.5 Vpp utilizing a brightness signal as a standard signal is provided to an FM circuit, the FM circuit must output a frequency signal having a sync tip level of 3.4 MHz.+-.0.1 MHz and a white peak of 4.4 MHz.+-.0.1 MHz (i.e., frequency deviation of 1.0 MHz.+-.0.1 MHz) with respect to the image signal provide. Even though IC's are designed with an accurate targeted level of electric characteristics, the fabricated IC's often fail to meet the target specifications.
A conventional technique for making a product meet a target specification involves using a variable resistor located outside an IC which is adjusted by the manufacturer of a product which uses the IC so as to control FM carrier & deviation and to provide a specific FM signal. A problem with this technique however, is that it increases the time and cost of manufacturing electric products such as VCRs.
Another conventional technique for adjusting the FM carrier & deviation of an IC involves cutting a fuse between both ends of a pad during the fabrication of an IC. However, even though the FM carrier & deviation are accurately adjusted during the fabrication of an IC, the electrical characteristics may change again during the following process steps after the adjustment thereof. As a result, a specific FM value still cannot be obtained in a fully assembled IC.
Accordingly, a need remains for a technique for adjusting an IC which overcomes the problems discussed above.